Production of chemically pure cobalt metal



Patented May 2, 1950 PRODUCT-ION F CHEMICALLYPURE GOBALT METAL Ch esL Mentell Menhasset Y-, s i nor'fi Reduction and h fi o en 14 Newark.- J., a corporation of New erse'y No Drawing, Application October 4, 1945, SerialiNo. 620,398

7 lClaino.

relate to the produ o 19f. Qhemi ahy e coba t pro uc s; ar eul r coba t powder, The enbelt'n w n t e marke ear-mir e balt is not uarantee o co ai more than 98 to"99 per cent of that metal. For many metallurgical uses cobalt powder having a purity ofatl east 99.9 per cent is in great demand.

Cobalt ores are usually treated so as to produce a im u e ox d ahd'th m u oxide may be re a ed s t e star n of my p oce It us ally eeht ins i v ryin mou s u metals .ekel, co ma g ne e a11 mimim and ee eiu eod a nu r o nommetah l e el ments uch as ul hur, hos s and silica.

A typi al analysis o obaltx de is ive below:

' Th s in en ion Nickel l 0.15 Gopper a 0.06 Manganese 0.16 on V 0 Aluminum Calc um 0.5 Sulphur ,0-125 insomp s (chieflysilica) 0.35

fiohalt products of Very high purity have 9f coursa'been preparedin thelaboratoiylfo etem e weight Bdeterminations and the like. In sugh eases! h w v a gh yield was no cons d a i solthat'the cobalt salt eb ld b re eatedly reerystel zed or cipitated a ed solved untilia small fraction of the original material has been brought to the desired degree of purity.

Commercially it is not practicable t st rt with 100 r minds of impure cobalt and end with!) to 10 poun s of u e cob lt.- Th p inci o je t therefore, of the present invention is to provide apmc ss y wh eh h hpur and high y e ca be btained-simu neo sly.

I ve ou ha these v esira e ob ect es can be obtained a two-stage impurity elimination process, using reagents whioh are gaseous or readily volatile by heating and which by reaction between themselves or' with water will produce readily volatile substances.

The firs tage i the n oo s eomp e pr eipitating the bull; .of the impurities, leaving'the cobalt in solution. The second stage comprises n ee i-te he t e oba t lea g the e n e 0,1. the impurities in solution.

I almo a y we n tien t ere i eh e of a ome e o ';Q l .l1 :h the 1 irates of such on? eihee abo 15 3 o he h mer precipitate he tot l moun entra n d d pen l r o the tot l amoun of re i e the heehlhh fihi imp it pr eih etesl in h fi st ta e sme relie v i' temp red wit the amount o eobah he less of co lt n ra n d so smell tha is not worthwhile t9 W sh the pre i at In 'the'see d stag h weve "the situation is .quite different Then the'precipi; ete me eri h h s es el l o r move i: tra ne hen vo atile m uri s This in ec ar l e u es e so elt The m a hhuntoi he 1w washing the I e he' emQv Y-hy l h'l s heeem l reeo volet elmhu. e e im h l h 'sh equent eat n o t ,,,...lh te. e eebe t 122 1.: w it is only he non-vo ati e im r tie h ve o h onsidered his was i st e 1 v using aseous or an volat le reesi hts e Qlh: sive the onl 'I 9I Qla E' mP-1l i ii ar t eentei ed in he i na mp re selh h- 'l-he most dvan a o s pr e u in es h us s re t of h r ehleri ac am nia m n um l ieelahd hlorine- The fa e! the r age ts use are ase- 11$ 9r rea l olatile hat t hen he o ta ned cemmer 1a1l ih-$ qh hi e o Pu ity tha the minute tra es Pi m h hr fheglig e elseihh CQWQYQ Q .P hy lQ lQ 5 than 0039 th t of leh o -i xe ss o 9.90 a i tha o zere Th sulhhhi cont ts as $51 rim 0.0002% for hydrochloric acid, 0.002% for ain monium chloride and .0.00 03.% for ammonia.

ther impurities such as phosphorus and heavv metals are of the same order of magnitude. Chlorine is also obtainable in a very high-state of urit .eepee esl re ards metal i purities.

fi'he er s ox de is t ea ed ihe qee 'q dr eh er ac d 9 i rm e oluhen o con -H9 Q 9- ride; 9 2 th smel a un Q'i'fi h i' 9 he be eh ii ed meta s lh 'e s S111- v m thi .fi hsij q h il ei'ee m he ne t p i to neutralize t eess' ih 'd er chl ri 'ee with e hzheh ey 11 iee th P efiili l flti nll i fi 9 h.e. t .h e xide 91 ha balt chloride is reached. Fur W amm ni ould hht hl he a t to hreeihi e e-whe ibut el e o -;r o some o 'ihenre ie .tated im u t es r. g sitiqhe reh anch, reeh e 1 thelh ee l tation of 93% lormo o the i o and lhll min no @1151 around 25% of the manganese. is filtered oif.

The partially purified cobaltous chloride is then converted into cobaltic chloro-pentammine. The first stage involving treatment by ammonia, ammonium chloride and chlorine.

Hydrochloric acid is then added to complete the formation of the chloro-pentammine and precipitate it, leaving the nickel and other impurities in solution. Cobaltic chloro-pentammine is a well known compound. Likewise it is known that its solubility decreases as the hydrochloric acid content of its solution increases. Also it is well known that procedures which form the cobaltic chloro-pentammine do not produce an insoluble nickel compound.

The precipitated ammine is then washed with hydrochloric acid to remove the greater part of the entrained nickel salts and other impurities still in solution.

The crude cobalt oxide is heated with hydro chloric acid in preference to sulphuric acid for various reasons. In the first place the pentammine contains chlorine so that a cobalt salt of any other acid than hydrochloric would have to be converted into cobalt chloride before the ammine could be formed. Second, the use of sulphuric acid would increase the sulphate content of the liquors and thereby also of the final precipitated ammine. In the heat treatment of the ammine or products derived from it any residual sulphate is very apt to be converted into cobalt sulphide-a highly detrimental impurity.

Other alkalies besides ammonia can be used to precipitate iron such as caustic soda, calcium hydroxide, etc., but not as advantageously as ammonia as the resulting sodium or calcium chloride is not volatile like ammonium chloride.

Directly or indirectly the cobalt has to be oxidized by chlorine to bring it from the cobaltous to the cobaltic condition. Where air or hydrogen peroxide is used as the oxidizing agent it reacts with some of the ammonium chloride present to form ammonia, water and chlorine. The latter immediately oxidizes the cobalt ammine to produce the cobaltic pentammine. Chlorine gas had the advantage over air that the oxidation proceeds more rapidly. From the point of view of purity or yield the use of chlorine has no advantage over air or hydrogen peroxide.

Chlorine is given off in the first step of the process in accordance with the following equation:

The same amount of chlorine is required for the production of the ammine.

(final product).

Hence the chlorine required from external, sources is only that needed to make up losses.

In the solution step, represented by Equation 1 above, the acid should be concentrated to save digestion time. At 20 B. solution (31.5% HCl by weight) is satisfactory. Appreciable excess of acid is not required, especially as a part of the chlorine liberated reacts with the Water present to form hydrochloric acid.

In a typical mode of carrying out the process 100 lbs. of raw cobalt oxide is digested with 420 lbs. of 20 B. acid (the theoretical amount called. for by Equation 1) in a glass-lined jacketed vessel with stirring for 3 hours at 75 C. and then for a further 3 hours at 100 C. The chlorine liberated This precipitate is passed into another vessel containing a previous batch of cobalt chloride and added reagents for oxidation of the cobalt from the cobaltous to the cobaltic condition.

The next step in the process is the precipitation of iron and aluminum and a part of the copper, manganese and other impurities. In this step high cobalt concentrations are to be avoided as tending to increase the liability of cobalt being precipitated along with the impurities, particularly as the solution is cooled prior to such precipitation.

After digestion is completed cold water is run. into the jacket of the digestor to cool its contents. At this stage the volume of liquor is slightly under gallons. To the cooled liquor prior to the addition of ammonia to precipitate the iron, etc., cold water is added to bring its volume up to 144 gallons. The concentration of cobalt is, therefore, around 6% at this stage. If the concentration is 15 much cobalt is precipitated before the pH has been raised to the point at which efiicient elimination of the impurities is obtained. Ordinarily the cobalt concentration should be under 7.5%.

The pH of the diluted liquor should be greater than 0.5. Large excess of acid should be avoided since the next step is to neutralize almost all of the acid. This is done by adding to the cooled liquor (around 20 C.) dilute ammonia water (1 part by volume 26 B. ammonia water plus 4 parts water) with vigorous stirring until the pH has reached 5.6 to 5.7. After standing 3 hours or more (e. g. overnight) a, slight further addition of dilute ammonia water with stirring is made to bring the pH to 5.8. After standing an hour or so the insolubles remaining from the acid digestion, chiefly silica and silicates, and the hydroxides and oxychlorides precipitated by the ammonia addition are filtered 011:.

With quantities of impurities similar to those given in the foregoing analysis the percentages of the'amounts originally present which are precipitated by the ammonia are about as follows:

The filtrate contains cobaltous chloride and a minor percentage of ammonium chloride produced by the neutralization of the hydrochloric acid, plus, of course, small amounts of nickel, manganese and copper, etc., not precipitated by the ammonia. The amount of ammonium chloride so formed should be around 5 lbs. or less. If the amount is greater the quantity of acid used in the digestion was excessive.

Where oxidizing agentsrother than chlorine are used, such as air or hydrogen peroxide, enough ammonium chloride must be used to supply one additional atom of chlorine for each atom of cobalt. When chlorine is used ammonium is advantageous but not essential. Its chief use is to increase the yield of the desired ammine. Another beneficial function of ammonium chloride is to aid the hydrochloric acid added later in reducing the solubility of the ammine.

I have found a suitable concentration of ammonium chloride in the liquor prior to the addition of the ammonia required for ammine production to be 5 to 6%. Hence, if the liquor contains 5 lbs. as the result of the neutralization of eateri- 69 the -hydrochloric acid=,' there should loea'ddekl a further 70 bibs to bring the concentration up Wl'ien the ammonium chloride has been dissolved=-ammonia water isaddedi The amount I is. advantageously about'50% in excessof that: theoretically required byEquation 2. That means adding 540 lbs. of 263 B. ammonia water. Where no ammonium-chloride is used the: amount of'i neutralor alkaline solution butmanybe thrown" out iof isolution nearly completely by adding-hydr'ochloric'acid." The amminebecomes less and less soluble' as the content of hydrochloric acid increases. There does not" appear to be any acid concentration at which the solubilityis a minimum. However, the rate of reduction of solubility falls off with increase in acid content so that a practical limit is reached with an acid concentration of around 15% HCl.

This concentration is produced by the addition of 230 gals. of 20 B. hydrochloric acid. This is equivalent to 700 lbs. of anhydrous hydrochloric acid. Of these 700 lbs. about 100 is consumed in neutralizing the 50 lbs. excess NH: (anhydrous) added prior to chlorination to produce 150 lbs. of ammonium chloride, in addition to the 75 lbs. already present.

At this stage the total volume of solution is approximately 460 gallons so that the cobalt content is around 1.6 to 1.7%. It is desirable to keep the cobalt concentration below 2% to reduce the occlusion of impurities by reducing their percentage content in entrained liquor. For example, the removal of calcium sulphate is greater in dilute than in more concentrated solutions. Further, the more concentrated solution the larger the crystals of ammine produced and the greater the difficulty of washing them free of occluded impurities.

Assuming complete precipitation of the 71 lbs. of cobalt in the form of pentammine, the mother liquor then contains approximately Pounds Hydrochloric acid 600 Ammonium chloride 225 Nickel chloride 0.33 Copper chloride 0.026 Manganese chloride 0.23 Calcium chloride 0.6 Calcium sulphate 1.0

It will be noted therefore that the non-volatile impurities are a very minor percentage of the total non-aqueous content of the mother liquor.

In precipitating the ammine some of the material in solution is unavoidably carried down with the precipitate either by adsorption or by entrainment of mother liquor. Assume that such adsorption or entrainment results in /50 of the solubles remaining in the precipitate, even after washing. Reduction of solubles of this order would not lower the ammonium chloride below 4.5 lbs. or 6.3% on the cobalt. However, as the ammonium chloride can be subsequently removed by volatilization, its presence, even in large amounts is immaterial. n the other hand, a similar reduction of nickel, for example, would ammonium chloride solutions otvariousstrengths :ouszto personnel. than: the hydrochloric acid; I

result 'in a-inickel content-of 0.0066 lb;- or 0i0l came cobalt.

The next step is to decant (or illterJ -then weeks the precipitate several times (by decantaticn and/ or washing on the-filter); n centrifugeimay bevused' fin aorraf-ter the-i'final washL-un :ordentdecrease the 1 amount a of adherent": liquor..- wash li'quorsmay be K hydrochloric. acid of ivari' ousaastrengths (ex-g; 510%. or? greater.) -and1o toe (e. g.. over 5*.0%--andv.preferably 10.0%). Their;- grea-teri the concentration.- of :acid ;.or ammoniuma chloride, tha-smaller 1'thB".10SS. in yieldi. Prefers ably xammonium: chloride I washes: area: used iexa clusively or atemostiaone. hydrochloric acidawashz;

followedzbyn ammonium chloride awash'es. Th e latter -at1t10% concentration: dissolves, an: exetremelyzsmalliamountzoi ithe cobalt .pentammine; and isiless injurious. to equipment andless-hazard also. .permitsremoval' of excessacidzwithout-largea:

loss 20f 2 yield .".obtained when water r is remployed'e:

to remove this excess;

The-.mother rliquor; may. be gplaced:v :in. .a;still;tms

. driveofi; the hydrochloriceacidcfor reeuseeandzi' at the same time raise the concentration of the ammonium chloride to around saturation. The liquor is then withdrawn and allowed to cool to crystallize out the greater part of the ammonium chloride for re-use, either with or without purification by sublimation.

The ammine is then converted into cobalt metal or some other compound of cobalt with the recovery of ammonia and ammonium chloride for re-use in treating subsequent batches of cobalt chloride.

Various methods may be used, one being the reduction of the dry ammine by hydrogen. The end products are probably essentially as represented below:

The ammine may be dried by passing warm air at 200 to 220 F, over trays containing the ammine. The dried ammine is then ground and placed in silica boats, which are then placed in a tubular furnace. Hydrogen is passed through the tube and over the boats while the temperature is gradually raised to 1000 F. to decompose the ammine and cause the reduction to cobalt'metal. The liberated ammonia and ammonium chloride may be collected for re-use.

It will be noted that not only are all the reagents used in going from the crude oxide to the metal either gaseous or readily vaporizable, but also their products are likewise gaseous or readily vaporizable, which permits their recovery for subsequent use. The chief by-product is ammonium chloride.

The reaction between the excess hydrochloric acid and ammonia in the iron precipitate step produces ammonium chloride. The chlorine also reacts in such a way as to ultimately produce ammonium chloride. The addition of excess hydrochloric acid to the ammoniacal ammine solution likewise forms ammonium chloride. Then, finally, the treatment of the dried ammine with heat treatment and hydrogen yields ammonia and ammonium chloride. As a result, the treatment of each batch yields considerably more ammonium chloride than was added during the course of such treatment. After recovery the excess may be converted into ammonia by the well known procedure of heating the ammonium chloride with lime. Ammonia, being gaseous, is

obtained free of lime and the impurities contained in the lime.

. What I claim is: V

' The process of producing substantially chemically pure cobalt metal which comprisestreating cobalt oxides with an excess of hydrochloric acid to'form a solution of cobaltous chloride; neutralizing the excess acid with dilute ammonia until nearthe precipitation point of the cobalt salts present and to a pH of about 5.6 to 5.7; allowing the mixture to stand until the precipitation of the bulk of the impurities has been completed, while maintaining a relatively low cobalt concentration of an order not substantially in excess of 7.5%, to prevent losses of cobalt material with the precipitating impurities; making a further slight addition of dilute ammonia water with stirring to bring thepH to approximately 5.8 and permitting the remaining insolubles, comprising silica, silicates, hydroxides and oxychloridesto precipitate; removing the impurities by filtration; and further adding ammonia in molecular proportion to convert the cobalt chloride to thecobalt-chloro-pentammine in the presence of cobalt, not substantially in excess of 2%;v

thereafter gradually addin hydrochloric acid to effect the precipitation of the pentammine, washing the same for removing adherent impurities and recovering the metal therefrom. CHARLES L. MANTELL.

REFERENCES CITED The following references are of record in the file of this patent:

Prescott & Johnson's Qualitative Chemical Analysis. 5th ed., p. 161.

Mellor, Comprehensive Treatise on Inorganic,

and Theoretical Chemistry, vol. 14, 1935, p.442. Treadwell and Hall, Analytical Chemistryff pp. 188-189, vol. 1. 7th ed. (1930).

Ephraim, Inorganic Chemistry, 4th ed., 1943, i

p. 315. P. C. L. Thorne and E. R. Roberts. 

